This invention relates to triazole derivatives useful in therapy (in particular in the treatment of fungal infections in humans and other mammals), methods for their use, formulations including them and processes for their production.
A large number of triazole antifungal compounds are known. For example, European Patent Application 0440372, Example 7, discloses (2R, 3S)-2-(2,4-difluorophenyl)-3-(5-fluoro-4-pyrimidinyl)-1-(1H-1,2,4-triazol-1-yl)-butan-2-ol (also known as voriconazole) which has particularly good activity against the clinically important Aspergillus spp fungi. However, the compound has low solubility in aqueous media, necessitating the use of complexing agents to achieve satisfactory aqueous formulations, such as intravenous formulations. European Patent Application 0440372 suggests co-formulation with cyclodextrin derivatives to improve solubility; however, it is always desirable to keep the number of ingredients in a formulation to a minimum so as to minimize possible adverse reactions in patients.
UK Patent Application 2,128,193 discloses phosphoric acid esters for use as plant fungicides and insecticides.
Maurin et al [Int J Pharm, 1993, 94(1-3), 11-14] disclose xcex1-(2,4-difluorophenyl)-xcex1-[(1-(2-(3pyridyl)phenylethenyl)]-1H-1,2,4-triazole-1-ethanol bismesylate, which is stated to be an antifungal agent having high solubility.
Other triazole antifungal agents are known from European Patent Application 0576201 and international Patent Application WO 97/01552.
European Patent Application 0413674 discloses formation of prodrugs of therapeutic glycosidase inhibitors by phophorylating a free hydroxy group in the molecule. However, phosphorylation of tertiary hydroxy groups is not described.
It has now been found that triazole antifungal compounds of the type comprising a tertiary hydroxy group, including (2R,3S)-2-(2,4-difluorophenyl)-3-(5-fluoro-4-pyrimidinyl)-1-(1H-1,2,4-triazol-1-yl)-butan-2-ol, may be converted into pro-drugs having greatly enhanced solubility, but which are converted readily in vivo to give the desired active moiety.
According to the invention, there is provided a compound of formula I,
R1xe2x80x94OP(O)(OH)2xe2x80x83xe2x80x83I
wherein R1 represents the non-hydroxy portion of a triazole antifungal compound of the type comprising a tertiary hydroxy group;
or a pharmaceutically acceptable salt thereof (referred to herein as xe2x80x9cthe compounds of the inventionxe2x80x9d).
The compounds of the invention are distinct from the prior art because the tertiary hydroxy group in triazole antifungal compounds of this type has not previously lent itself to functionalization.
Pharmaceutically acceptable salts that may be mentioned include alkali metal salts of the phosphate group, for example disodium or dipotassium salts; and salts with an amine counter ion, for example ethylenediamine, glycine or choline salts.
Preferably, R1 represents a group of formula Ia, 
in which
R2 represents phenyl substituted by one or more halogen atoms;
R3 represents H or CH3;
R3a represents H, or together with R3 it may represent xe2x95x90CH2; and
R4 represents a 5- or 6-membered nitrogen-containing heterocyclic ring which is optionally substituted by one or more groups selected from halogen, xe2x95x90O, phenyl [substituted by a group selected from CN and (C6H4)xe2x80x94OCH2CF2CHF2] or CH=CHxe2x80x94(C6H4)xe2x80x94OCH2CF2CHF2; or phenyl substituted by one or more groups selected from halogen and methylpyrazolyl.
When R1 represents a group of formula Ia, as defined above, R2 is preferably 2,4-difluorophenyl, and R3 is preferably H or methyl.
Nitrogen-containing heterocyclic rings that R4 may represent or comprise include triazolyl, pyrimidinyl and thiazolyl.
Preferred specific groups that R1 may represent include: 
The triazole antifungal compounds corresponding to the groups (a)-(g) above are: (a) D-0870 (under development by Zeneca, see also Example 19, European Patent Application 0472392); (b) fluconazole (sold by Pfizer, see also UK Patent Application 2099818); (c) Example 7 of European Patent Application 0440372, also known as voriconazole; (d) Example 35 of U.S. Pat. No. 4,952,232; (e) the compound of Example 8 of the present application; (f) Compound A of WO 95/22973 (see page 29), originally disclosed as Compound 30 in Example 27 of EP 567982; and (g) ER-30346 (see Drugs of the Future, 1996, 21(1): 20-24, Tetrahedron Letters, Vol 37, 45, pp 8117-8120, 1996 AND European Patent Application 0667346, Example 88).
The present invention also provides a process for the production of a compound of formula I, as defined above, or a pharmaceutically acceptable salt thereof, which comprises phosphorylating a compound of formula II,
R1OHxe2x80x83xe2x80x83II
wherein R1 is as defined above;
and where desired or necessary converting the resulting compound into a pharmaceutically acceptable salt or vice versa.
The phosphorylation may be carried out using the following steps (1)-(3):
(1) Reacting a compound of formula II, as defined above, with a compound of formula III,
RaRbNxe2x80x94P(ORc)(ORd)xe2x80x83xe2x80x83III
wherein Ra and Rb independently represent C1-6 alkyl, phenyl or substituted phenyl, or together with the nitrogen atom to which they are attached they may represent a ring such as a morpholine ring; and Rc and Rd independently represent hydroxy protecting groups selected from benzyl optionally subsituted by one or more halogen atoms; to give a phosphite compound of formula IV,
Rixe2x80x94Oxe2x80x94P(ORc)(ORd)xe2x80x83xe2x80x83IV
wherein Ri, Rc and Rd are as defined above.
The reaction may be carried out in a solvent which does not adversely affect the reaction (e.g. methylene chloride) in the presence of a mild acid (for example tetrazole, 5-methyltetrazole or pyridinium hydrobromide) and optionally 4-dimethylaminopyridine, at room temperature or above.
(2) Reacting the resulting phosphite of formula IV with an oxidant (for example a peracid such as 3-chloroperoxybenzoic acid, or H2O2), to give a phosphate of formula V,
R1xe2x80x94OP(O)(ORc)(ORd)xe2x80x83xe2x80x83V
wherein R1, Rc and Rd are as defined above. The reaction may be carried out in a solvent which does not adversely affect the reaction (e.g. methylene chloride or ethyl acetate) below room temperature (for example 0-xe2x88x9220xc2x0 C.).
(3) Removing the hydroxy protecting groups from the compound of formula V to give a compound of formula I, as defined above.
As an alternative to step (1), phosphites of formula IV may be prepared according to steps (1A) and (1B):
(1A) Reaction of a compound of formula II, as defined above, with PCl3 in the presence of a base to give a postulated intermediate compound of formula VI,
R1xe2x80x94Oxe2x80x94PCl2xe2x80x83xe2x80x83VI
wherein R1 is as defined above. The reaction may be carried out in a solvent which does not adversely affect the reaction (e.g. methylene chloride or ethyl acetate) at a temperature in the range xe2x88x9220 to +20xc2x0 C. (for example 0xc2x0 C.). Suitable bases include pyridine and N-methylimidazole.
(1B) Reaction of the compound of formula VI with a compound of formula RcOH and/or RdOH (in which Rc and Rd are as defined above) to give a compound of formula IV, as defined above. The reaction is performed without isolation of the compound of formula VI, at a temperature around room temperature.
Hydroxy protecting groups which Rc and Rd may represent include 2,6-dichlorobenzyl and 2-chloro-6-fluorobenzyl. Benzyl groups may be removed using catalytic hydrogenation (e.g. over Pearlman""s catalyst or palladium-on-carbon) or bromotrimethylsilane.
If step(3) is carried out in the presence of sodium acetate or sodium hydroxide, the disodium salt may be obtained directly.
Process step (3) above, and the intermediate compounds of formula V from further aspects of the invention. Compounds of formulae II and III are either known or are available using known techniques.
It will be apparent to those skilled in the art that sensitive functional groups may need to be protected and deprotected during synthesis of a compound of the invention. This may be achieved by conventional techniques, for example as described in xe2x80x98Protective Groups in Organic Synthesisxe2x80x99 by T W Greene and P G M Wuts, John Wiley and Sons Inc, 1991.
The compounds of the invention are useful because they possess pharmacological activity in animals, including humans. In particular, the compounds are useful in the treatment or prevention of fungal infections. For example, they are useful in treating topical fungal infections in man caused by, among other organisms, species of Candida, Trichophyton, Microsporum or Epidermophyton, or in mucosal infections caused by Candida albicans (e.g. thrush and vaginal candidiasis). They can also be used in the treatment of systemic fungal infections caused by, for example, species of Candida (e.g. Candida albicans), Cryptococcus neoformans, Aspergillus flavus, Aspergillus fumigatus, Coccidioides, Paracoccidiodes, Histoplasma or Blastomyces.
Thus, according to another aspect of the invention, there is provided a method of treatment or prevention of a fungal infection which comprises administering a therapeutically effective amount of a compound of the invention to a patient. The use of the compounds of the invention as pharmaceuticals, and the use of the compounds of the invention in the manufacture of a medicament for the treatment or prevention of fungal infections are also provided.
The in vitro evaluation of the antifungal activities of the compounds of the invention can be performed by determining the minimum inhibitory concentration (m.i.c.), which is the concentration of the test compounds, in a suitable medium, at which growth of the particular micro-organism fails to occur. In practice, a series of agar plates, each having the test compound incorporated at a particular concentration, is inoculated with a standard culture of, for example, Candida albicans, and each plate is then incubated for 48 hours at 37xc2x0 C. The plates are then examined for the presence or absence of growth of the fungus and the appropriate m.i.c. value is noted. Other micro-organisms used in such tests can include Aspergillus fumigatus, Trichophyton spp., Microsporum spp., Epidermophyton floccosum, Coccidioides immitis and Torulopsis glabrata. 
Some compounds of the invention, although active in vivo, may not demonstrate activity in these in vitro tests.
The in vivo evaluation of the compounds of the invention can be carried out at a series of dose levels by intraperitoneal or intravenous injection, or by oral administration, to mice which are inoculated with, e.g. a strain of Candida albicans or Aspergillus fumigatus. Activity is based on the survival of a treated group of mice after the death of an untreated group of mice. The dose level at which the compound provides 50% protection against the lethal effect of the infection (PD50) is noted. For Aspergillus spp. infection models, the number of mice cured of the infection after a set dose allows further assessment of activity.
For human use, the compounds of the invention can be administered alone, but will generally be administered in admixture with a pharmaceutically acceptable carrier selected with regard to the intended route of administration and standard pharmaceutical practice. For example, they can be administered orally in the form of tablets containing such excipients as starch or lactose, or in capsules or ovules either alone or in admixture with excipients, or in the form of elixirs, solutions or suspensions containing flavouring or colouring agents. They can be injected parenterally, for example, intravenously, intramuscularly or subcutaneously. For parenteral administration, they are best used in the form of a sterile aqueous solution which may contain other substances, for example, enough salts or glucose to make the solution isotonic with blood.
For oral and parenteral administration to human patients, the daily dosage level of the compounds of the invention will be from 0.01 to 20 mg/kg (in single or divided doses) when administered by either the oral or parenteral route. Thus tablets or capsules of the compounds will contain from 5 mg to 0.5 g of active compound for administration singly or two or more at a time, as appropriate. The physician in any event will determine the actual dosage which will be most suitable for an individual patient and it will vary with the age, weight and response of the particular patient. The above dosages are exemplary of the average case; there can, of course, be individual instances where higher or lower dosage ranges are merited, and such are within the scope of this invention.
Alternatively, the compounds of the invention can be administered in the form of a suppository or pessary, or they may be applied topically in the form of a lotion, solution, cream (for example comprising an aqueous emulsion of polyethylene glycols or liquid paraffin); or they can be incorporated, at a concentration between 1 and 10%, into an ointment consisting of a white wax or white soft paraffin base together with such stabilizers and preservatives as may be required.
Thus, according to another aspect of the invention, there is provided a pharmaceutical formulation including preferably less than 50% by weight of a compound of the invention in admixture with a pharmaceutically acceptable adjuvant, diluent or carrier. Aqueous intravenous formulations are of particular interest.
The invention is illustrated by the following Examples.